All layer 3 isdn signaling is backhauled to call manager, so there shouldn't be any delay...but for some reason, in the case of 151-M1, you can see the message isn't being backhauled to CUCM, causing the T313 timer to fire.

Just a question if you allow please, when you were facing the issue that the router wasnot backhauling the connect act message to CUCM; did you see the message on the debug isdn q931 "and not in CUCM trace" or you were not seeing it at all in either places?